I'm the environment editor at Forbes. Before joining Forbes in April 2011, I wrote about all things green and tech as a contributor to The New York Times, a senior editor at Fortune and an assistant managing editor at Business 2.0 magazine. I previously was the business editor at the San Jose Mercury News and during the (first) dot-com era served as a senior writer and senior editor at The Industry Standard (RIP).

Secret Ingredient To Making Solar Energy Work: Salt

The solar thermalpower plant business is all about big: Square miles of mirrors in the desert that surround 600-foot-tall towers to generate massive megawatts of electricity for multibillion- dollar price tags. Big Solar’s ability to compete against fossil fuels, though, could come down to grains of salt.

In a small lab in the San Francisco Bay Area biotech hub of Emeryville, scientists at a startup called Halotechnics are sifting through thousands of mixtures of molten salt. They’re searching for the right combinations that will allow solar thermal energy to be stored cheaply and efficiently so it can be dispatched to generate electricity after the sun sets. In other words, the 24/7 solar power plant.

Molten salt storage has been around since the 1990s, when United Technologies’ Rocketdyne division developed it for Solar Two, a prototype “power tower” station built by the U.S. Department of Energy in the Mojave Desert. Arrays of mirrors called heliostats focus the sun on a boiler filled with salt that liquefies at high temperatures. The heat released by the molten salt is used to create steam that drives an electricity-generating turbine. Some of that heat can be held in tanks of molten salt and released when needed to produce electricity.

But as oil prices plunged in the Clinton era, the U.S. abandoned its grand solar experiment, and molten salt technology got shoved into cold storage. “There hasn’t been a heck of a lot of innovation in the technology,” says Mark Mehos, a veteran solar program manager at the National Renewable Energy Laboratory in Golden, Colo.

Now salt is back on the table as states such as California green-light big solar thermal power projects to meet ambitious renewable energy mandates. Utilities want those power plants to store solar energy so it can be used to balance a power grid increasingly supplied by intermittent sources of electricity like wind farms. GTM Research estimates solar energy storage will be a $3.7 billion market by 2015.

Justin Raade, Halotechnics’ 34-yearold founder and chief executive, saw an opportunity. A newly minted Ph.D. in mechanical engineering, Raade was working at a Silicon Valley materials science company called Symyx in 2009. “I was looking for a big problem to tackle in renewables, and the more I read about concentrated solar power the more I realized that energy storage was a bottleneck that kept it from being cheaper than fossil fuel,” he says.

His idea: a better molten salt mixture that would store heat at higher temperatures to boost electricity production but that would remain liquid at lower temperatures so less energy would be diverted to keep it from solidifying.

Raade secured a $1.5 million Department of Energy grant and in 2009 began screening 5,000 different salt combinations at Symyx. Raade started Halotechnics with an investment from Symyx and a license to its intellectual property. The startup tapped another $4.5 million in government research grants to develop its first molten salt product as well as begin work on a novel liquid glass storage system. “We’ve developed a new oxide-based chemistry that has a much lower viscosity and a much lower melting point than other glass materials. You can actually pump it like a liquid and store it in a big tank like you do with molten salt. But it’s stable at a much higher temperature.”

Higher as in 1,200 degrees Celsius, which would heat air hot enough to run a high efficiency turbine like those used in fossil fuel power plants. In the lab Raade picks up paper cups containing globs of green and black glass, two promising mixtures that Halotechnics hopes eventually to use in a prototype energy storage system the company plans to bring online in 2015.

Elsewhere in the lab, Halotechnics continues to sift through nearly 100 salt combinations a day—some 14,000 so far. Current molten salt mixes are typically 60% sodium nitrate and 40% potassium nitrate. Halotechnics aims to replace 80% of the increasingly costly potassium nitrate with materials it will describe only as “abundant, low-cost salt components.”

Post Your Comment

Post Your Reply

Forbes writers have the ability to call out member comments they find particularly interesting. Called-out comments are highlighted across the Forbes network. You'll be notified if your comment is called out.

hi, great day just was going through websites like this are very good. Here I found an excellent www.priority-1.com We talk about many issues such as enthusiasm, “When a person is charged with excitement, feel the need to infect others and that is my case” I recommend you let him and if you enter I like to click on the home page

Why not think small and instead of these mammoth units, developing a unit that takes care of the needs of one home at a time. Instead of installing a furnace and oil tank why not a self-contained unit that contains the molten salts and a steam powered generator like this unit (http://www.cyclonepower.com/index.html heating the water to make steam without burning fuel) that would be able to hold enough heat energy for a week to 10 days without sunlight. I figure you would need about 500 square feet of reflected sunlight to generate the power needed and stored as heat (750,000 BTU per day or 7,500,000 Btu for 10 days which is 2.2 megawatts {includes car charging}) for a family of 5. You would need a tank or highly insulated vessel of about 50 cubic feet (4 x 4 x 3) to hold that many BTUs with these salts.